Inverter circuits which include inductive elements feed back harmonics into the power network. In order to prevent degradation of the wave forms in the power network, it is usually necessary to include a passive or active harmonic filter in the inverter circuit. Some inverter circuits include an oscillator circuit which may be supplied from the rectifier through a network which provides for voltage maintenance; they are also referred to as "step-up converter circuits" and, typically, include a controlled element, such as a transistor, in a circuit with energy storage devices such as an inductance and a capacitor. The transistor is pulsed to provide for storage of energy in the energy storage devices to be released to bridge gaps in energy supplied during drop in input voltage.
The controlled element, typically the transistor, requires control from a clock source in order to limit the harmonics in the current taken up from the a-c power network to values which are acceptable to the power company, and/or to communication companies which may be affected by excessive harmonics in the power supply. Such standards are known and one such standard is that published by the German Society of Electrical Engineers, VDE 0712.
Circuits which control the switched transistor usually were separately provided for this transistor. The wave form of such circuits also has to be controlled so that it is essentially sinusoidal. All this requires complex external control circuitry.
Step-up converters and the like, also referred to as boost converters, since the output voltage can be greater than the input voltage, are known and described, for example, in the printed publication "Siemens Schaltnetzteile (SNT), Technik und Bauelemente, Technische Mitteilung", pp. 14-15, published March 1985, and also available in the English translation entitled "Switched-Mode Power Supplies (SMPS), Technology and Components, Application Note", published in English in August 1985. A step-up converter circuit with specific provision for sinusoidal control is described in British Patent No. 2,022,943, Haberzeth (assigned Siemens, Fed. Rep. Germany). A step-up converter, which does not have any special control circuit for sinusoidal wave form and adapted as an accessory or auxiliary circuit for fluorescent lamps is described in the referenced literature: "Neue Leuchten und Vorschaltgerate mit reduzierter Anschlussleistung" ("New Lamps and Auxiliary Circuits with Reduced Power Take-Up"), SIEMENS Energietechnik ("Energy Technology") 3, 1981, Issue 5. The circuit includes a step-up converter connected as a harmonic filter and a push-pull frequency generator to provide lamp energy. The current wave form accepted from the network is roughly triangular, and meets power company and engineering standard requirements with respect to the harmonics. The circuit utilizes different clocking or control frequencies for the step-up converter transistor and for the push-pull amplifier. It has been found that interferences arise in this type of operation.
The basic and known operation of step-up converters can be derived from any well-known literature relating to switched circuits and, for example, also from the referenced literature: O. Macek: "Schaltnetzteile-Motorsteuerungen" ("Circuit Components--Motor Controls"), Huthig, publishers.